Apparatus for determining the burning rates of solid rocket propellants



3,267,721 BURNING LANTS Aug. 23, 1966 K. H. JACOBS ETAL APPARATUS FORDETERMINING THE RATES OF SOLID ROCKET PROPEL 2 Sheets-Sheet 1 Filed Nov.15. 1963 5 1 W 5 1D mmkm N a s 5 R m rmm mHPE Jr whi e m w m s h Q P K 0United States Patent "ice APPARATUS FUR DETERMINING THE BURNING RATES 9FSQLID ROCKET PROPELLANTS Kenneth H. Jacobs, Redlands, Calif., and JosephPinsky, Skokie, and Philip Rosenberg, Highland Park, Ill., assignors tothe United States of America as represented by the Secretary of the ArmyFiled Nov. 15, 1963, Ser. No. 324,142 1 Claim. (Cl. 7335) This inventionrelates to the design of an apparatus for determining the burning ratesof solid rocket propellants or similar materials at various pressures.

The use of solid propellants in the rocket and missile field iswidespread and particularly in the field of rocket assisted projectilesand boosters. In order to be able to accurately predict the performanceof such devices it is necessary to know the burning rates of the solidpropellants at various pressures. The pressures at which the propellantburns in use depends upon the design of the particular rocket in whichit is used.

Previous research has been conducted in which the burning rates of solidpropellants at relatively low pressures were determined using differentgaseous atmospheres to develop the pressures. These tests establishedthat the burning rates were substantially diiferent for differentgaseous atmospheres. In view of this it is apparent that it is necessaryto establish burning rates by burning the propellants in an atmosphereof their own gases as would occur in operation.

The apparatus of this invention is comprised essentially of an expansionchamber, a smaller elongated test chamber adjoining the expansionchamber, a number of timing devices fastened at intervals along thelength of the test chamber, a pressure gauge and means for igniting thepropellant to be tested.

An object of the invention is to provide a testing device fordetermining the burning rate of solid propellants.

Another object of the invention is to provide a testing device fordetermining solid propellant burning rates at different pressures.

Another object of the invention is to provide a testing apparatus forsolid propellants having a pressure measuring means and spaced timingmeans to measure the rate of burning of the propellants.

Yet another object is to provide a testing device for determining therate of burning of solid propellants in an atmosphere of their owngases.

These and other objects of the invention will be more apparent whenreference is had to the following detailed description and drawing inwhich:

FIGURE 1 is an axial sectional view of the test apparatus,

FIGURE 2 is a schematic diagram of the apparatus for recording thepressure and rate of travel of the flametront, and

FIGURE 3 is a schematic showing of one part of the thyratron bridge ofFIGURE 2.

The test apparatus or burning rate bomb of the present inventioncomprises in general two sections, an expansion chamber section and apropellant and test chamber section.

The expansion chamber section is indicated in general in FIGURE 1 byreference character 1 and has a generally cu-p shaped body 2. The body 2is externally threaded at 3 and is counterbored at 4 and furthercounterbored at 5. Extending through the body at spaced points are theapertures 6 and 7. Threaded into the aperture 6 is the pressure gauge 8which may be of any known type, such as for example, an electricalresistance ferrule type. The aperture 7 threadedly receives the ignition3,267,721 Patented August 23, 1966 member which has the body portion 9and the sealing washer 10 is clamped between the ignition member andexpansion chamber body 2. Ignition current is carried through conductingrod 11 which is insulated from the body portion 9 by Micarta 12. Theground connection for the igniter is indicated at 13 and is connected tothe stud 14 which is carried by the body 2 of the expansion chamber.

The propellant and test chamber section is indicated in its entirety at15 and is generally bottle shaped. The larger end of this chambercarries the flange 17 which is received in the bore 4 of the expansionchamber. The sealing ring 18 is mounted between the flange 17 andexpansion chamber body 2 in the counterbore 5 and the chambers areclamped together by means of the threaded member 19.

The body portion of the propellant and test chamber is enlarged at 20 toform the large diameter chamber 16 which forms a part of the expansionchamber and has the reduced elongated neck section 21 which forms thesmall diameter test chamber 22. The end of the test chamber is sealedoff by threaded cap 23 and sealing washer 24. Threaded into the neckportion 21 at axially spaced points are the three timing terminals 25which communicate with the test chamber by means of apertures 26. Eachtiming terminal includes a central conductor rod 27 having a headportion 28 which is insulated from the body portion by Micarta 29.

Operation In operation a quantity of solid propellant P is placed intest and propellant chamber 15 so as to fill the test chamber 22 and atleast partially fill the enlarged chamber 16. The quantity is varied andit has been found that by varying the distance S different pressures canbe obtained within the bomb. The bomb is then closed and sealed and theignition member 9 fired. By use of a small quantity of black powder orthe like this ignites the solid propellant P. It has been found that dueto the large size of chamber 16 and the relatively small size of chamber22 that the propellant in expansion section 16 burns and produces acertain pressure in the two sections and after the flame front hasentered the relatively small volume of test chamber 22 the subsequentpressure rise is small and the test portion of the propellant burns atan essentially constant pressure. The pressure attained is measured bypressure gauge 8.

As the propellant burns ionic gases are formed and these gases areeffective to close the circuit between the timer conductor heads 28 andthe bomb case 21 which is grounded. Thus, as the flame front travelsalong the test section chamber 22 the circuits including the timingterminals are successively closed and by accurately measur ing the timeinterval between closing of these circuits and knowing the distancebetween the terminals the rate of burning can be accurately determined.

FIGURE 2 illustrates a circuit for recording the pressure and time ofclosing of the timing terminals. There is provided a two channeloscilloscope recorder 30 and the oscilloscope screens are photographedby a high speed camera. The pressure gauge 8 is of the electricalresistance ferrule type and is one leg of a Wheatstone bridge. Thesignal from this bridge is applied to one channel of the oscilloscoperecorder through line 31. The burning rate bomb body is grounded asindicated at 32. At 33 there is schematically shown the oscilloscopecontrol and power supply. A thyratron bridge is shown at 34 and leads 35connect the timing elements 25 to the bridge. Batteries 36 are includedin the lines 35. Successive signals from the thyratron bridge areconducted through line 37 to the second channel of the oscilloscoperecorder.

FIGURE 3 shows the timing circuit which forms a part of the circut shownin FIGURE 2. The potential at point A is held at minus 9 volts by thebattery 40. The thyratron tube is set to fire at minus /2 volt. When thecircuit is closed by the presence of ionized gases at timing terminal 25the thyratron will fire since the potential at A will be about plus 67/2 volts as applied by the battery 39. The firing of the thyratron tubeis then recorded on the oscilloscope as a break in the line. Thethyratron bridge 34 as shown in FIGURE 2 will contain three of thecircuits as shown in FIGURE 3 for the three timing terminals, eachproviding its signal to line 37.

An alternative method for measuring the timing is to connect each timingterminal by way of a resistance to a balanced Wheatstone bridge. Whenthe timing terminals are closed by the ionized gases the bridges areunbalanced and provide signals. In this arrangement separateoscilloscope channels are required for each timing terminal.

It will be apparent that the embodiment shown is only exemplary and thatvarious modifications can be made in construction and arrangement withinthe scope of the invention as defined in the appended claim.

We claim:

An apparatus for determining the burning rate of a propellant comprisingin combination, a cup shaped body forming a first part of an expansionchamber and having external threads and a counterbore at its open end, atubular body having open ends and adapted to receive a solid propellantfor testing therein, said tubular body defining an enlarged portionadapted to fit snugly within said first part of said expansion chamberand forming the second part thereof, said tubular body diverging towardsone end to form an elongated test chamber of uniform dimensionthroughout and of smaller diameter than said second expansion chamberpart, there being an external, annular flange on said tubular body andbeing disposed adjacent said divergence, said flange adapted to fitsnugly within said counterbore in said cup shaped body, sealing meansbetween said flange and said cup shaped body, a threaded collar adaptedto tightly secure said tubular body in said cup shaped body, a closurecap for threadalble engagement with said elongated test chamber,pressure sensing and igniting means in said expansion chamber, a seriesof longitudinally spaced, timing terminals in communication with saidelongated test chamber, each terminal including a member threadablysecured therein and a conductor carried by and insulated from saidmember whereby ionic gases caused by combustion of said propellant iseffected to form a closed electric circuit between said conductor andsaid test chamber, and electric circuitry in connection with saidpressure sensing means, said igniting means and said terminals, saidcircuitry including a power supply for energizing said igniting meansand indicating pressure from said pressure sensing means, and means insaid circuitry for recording the time of said closing of an electriccircuit by said ionic gases including a thyratron tube connected to eachsaid conductor in each said terminal and fired by said circuit closingand an oscilloscope connected to said thyratron tubes.

References Cited by the Examiner UNITED STATES PATENTS 2,395,902 3/1946Nisewanger et al. 7335 X 2,925,729 2/1960 OBrien 73-35 3,191,426 6/1965Wilhite et al. 7335 RICHARD C. QUEISSER, Primary Examiner. JAMES J.GILL, Examiner.

